Packet switches are designed to avoid collisions of the packets of data that are being switched. Collisions of data packets occur within a switch when two data packets arrive at the inputs to the switch at the same time and are destined for the same switch output. While the switching mechanism can switch one packet to the appropriate output, the other data packet cannot be accommodated by the switching mechanism. The second data packet consequently is blocked from reaching its destination. As a result, the second data packet is destroyed and data are lost.
Optical packet switches are switches which switch data packets in the optical domain. Data packets remain as optical signals throughout the entire switching process. Optical packet switches, like other packet switches, are designed to avoid data packet collisions.
One common technique for avoiding packet collisions in an optical packet switch is to switch contending data packets into optical recirculation storage devices such as recirculating loops. An optical recirculating loop stores an optical data packet by confining the data packet in a loop of optical fiber until such time as it is desirable to extract the data packet from the loop. The stored data packets can be retrieved at a convenient time, such as when a contention no longer exists within the switch. In this way, a packet that otherwise would be destroyed is stored in the recirculating loop.
Recirculation storage devices, however, are prohibitively expensive to use. For example, recirculating loops require complex switching and control circuitry to function properly. Moreover, each recirculating loop must be provided with means for optically amplifying the recirculating data packet to compensate for losses resulting from recirculation and switching. Optical amplification adds expense and complexity to the system. It therefore would be desirable to provide an optical switch which switches data in the optical domain, but which does not rely on recirculation storage devices.